In recent years, along with the progress in downsizing and sophisticating of various kinds of electronic devices such as video recorder or personal computer, a compact and low-profile detection switch capable of operating reliably is required to detect presence or absence of storage media or operating condition of mechanisms such as knobs or inlet doors.
A conventional switch is described with reference to FIGS. 4 and 5. FIG. 4 shows a cross-sectional view of the conventional switch. In FIG. 4, the conventional switch has a substantially box shaped open-topped casing 1 formed from insulating resins and a plurality of fixed contacts formed of a conductive thin metal sheet implanted secured on the internal bottom surface of casing 1 with terminals (not shown) extending outward respectively.
Lever 3 formed from insulating resins is housed in casing 1 pivotally with fulcrum 3A at the left end to act as a supporting point. Lever head 3B projecting upward from the top surface of casing 1 is formed at the right end. Movable contact 4 formed of a resilient thin metal sheet is secured on lever 3 with holder 4B at the right end of arm 4A molded inserted on the internal bottom surface of lever head 3B. A substantially arc-shaped contact-part 4C formed on the left end of arm 4A in a slightly bent condition comes into resilient contact with the internal bottom surface of casing 1. Cover 5 formed of a thin metal sheet covers the opening of the top surface of casing 1 and lever head 3A of lever 3 is projecting upward from through-hole 5A of cover 5.
The switch with the above configuration is disposed on a printed circuit board (not shown) with a plurality of wiring patterns formed on its top and bottom surfaces. The terminals extending from fixed contacts 2 are connected electrically with the given wiring patterns of electronic circuits (not shown) of the device by soldering.
FIG. 5 shows a cross-sectional view of the conventional switch in operation. In this configuration, when lever head 3B projecting upward from casing 1 is pushed downward by inserting or extracting storage media such as tapes or discs, or by moving of mechanisms such as knobs or inlet doors, lever 3 pivots downward with the top surface of fulcrum 3A to act as a supporting point as shown in the cross-sectional view in FIG. 5. Along with the pivoting of lever 3, arm 4A of movable contact 4 bends further and contact-part 4C on the left end of arm 4A slides leftward to the direction of fixed contact 2 coming into resilient contact with the internal bottom surface of casing 1. After lever head 3B moves downward a given amount of distance, contact-part 4C comes into resilient contact with fixed contact 2, connecting a plurality of fixed contacts 2 electrically via movable contact 4.
When lever 3 is released from the pushing force, from the state of lever head 3B having been brought into contact with the internal bottom surface of casing 1 by a pivoting operation to the end, lever 3 is then pushed upward to pivot by a restoring force of movable contact 4. Contact-part 4C also slides rightward from fixed contact 2 coming into resilient contact with the internal bottom surface of casing 1 to return to its original state as shown in FIG. 4. Namely, fixed contacts 2 are electrically disconnected from movable contact 4.
Through the electrical connection or disconnection of the switch, the electronic circuits of a device is to detect the presence or absence of storage media such as tapes or discs, or the operating condition of mechanisms such as knobs or inlet doors.
At this time, the resilient restoring force of movable contact 4 to return lever 3 to its original state becomes larger, as the larger the inclined angle θ of the center of contact-part 4C to the top surface of fulcrum 3A at the left end of lever 3, the larger the force acting rightward on contact-part 4C or component of force to the returning direction, enabling lever 3 to return reliably as shown in FIG. 5.
Namely, when arm 4A of movable contact 4 is shortened and the center of contact-part 4C is moved rightward, the inclined angle θ can be larger, which will increase the restoring force of lever 3. In such a case of shortened dimension of arm 4A of movable contact 4, however, the bending amount of arm 4A would also varies, causing a decrease in the force for contact-part 4C to push fixed contact 2 resiliently or so-called contact-pressure.
Therefore, it has been difficult to develop a compact and low-profile switch entirely keeping a stable electrical connection or disconnection as a switch while both the restoring force of lever 3 and contact-pressure on fixed contact 2 are maintained. Following Patent document 1 is known as an example of the Information Disclosure Statement (IDS) for the present invention:    [Patent document 1] Japanese Patent Unexamined Publication No. 2006-318851